The invention is shown and described with respect to a magnetic hard disk data storage file, but is adaptable to the control of most dynamic systems. A dynamic system is subject to variations based upon manufacturing tolerances of the device, its assemblies and components. The system is subject to change in operation as a result of environmental conditions such as temperature and humidity and operating conditions such as position within the cycle of operation. Finally, the system is subject to variations induced by wear and age.
Compensation can be made for manufacturing tolerances and component differences by factory tuning or adjustment. However, this is only partially effective, since many factors such as operating and environmental conditions cannot be accommodated by such procedures. In addition, age and wear can be a factor by imparting an early change in the life of the product as the system is altered by early operation or run in.
The environment in which the invention is shown and described is a voice coil motor driven actuator for a rigid magnetic disk data storage device. These devices require great precision to meet specification requiring more than 1000 tracks per inch and information bit densities exceeding 12,000 bits per inch. This can not be accomplished by designing to worst case mechanical and electrical component tolerances, operating environments and wear to be experienced during product life.
The actuator that carries the magnetic transducers is an electro-mechanical system with numerous components that are subject to variation. The heads have parameters such as core width and gap length. There is a demodulator gain and an actuator mechanical force constant. There are analog to digital and digital to analog gains and actuator predriver and power driver gains. The mass variation between apparently identical actuators, the sampling period and the track pitch must be accommodated. All of these parameters are subject to change as a result of factors including temperature, humidity, wear and initial tolerances.
One option available for over coming these problems is to limit the performance standard to that of the least capable device that marginally attains the standard of acceptability. Another is to raise the level of all devices by holding rigorous tolerances with a corresponding high component rejection rate and increased cost.